Matching crank case to cylinder

[Vmakgp]

Afternoon chaps' I'm looking at matching my small block casing to my GT 186 kit I've marked out on cylinder gaskit face and at the minute the walls are around 7..5 to 8mm I've used the ally packer supplied wich is a decent match to the ports on the GT barrel but I'm reluctant to fully match them as it would take the casings down to 5 mill or just under, so do I not bother at all , or would it be worth maybe taking around 1.5 to 2mm out ? I'm fitting the new GT 60/110 stroke crank and there fore will be using a packer & was worried about taking the width of the gasket face down to much .
Any advise much appreciated .

[Warkton Tornado No.1]

Ha!

I think that most of us that port crankcases to cylinders are happy if we have as much as 3 mm remaining!

The seal should be fine as long as you use a good product between faces.

I hope that helps….

[Vmakgp]

Ha!

I think that most of us that port crankcases to cylinders are happy if we have as much as 3 mm remaining!

The seal should be fine as long as you use a good product between faces.

I hope that helps….

Thanks Tornado for the reply .

[bazza3004]

Hi Vmakgp like many others i matched my old GT 186 kit to my small block casing infact i opened the barrel and casing a litttle bit more than standard and had no trouble at all with less casing width than you have. I didnt use a base gasket on my set up just a good quality sealent and as i say never had any problems down there.

[Scooter Paul]

I have had a problem in the past with a paper gasket being sucked in. Now I use an alloy gaskets with a much larger surface area.
Paul.

[Vmakgp]

Cheers 'chaps got the die grinder out today & got stuck in , hopefully get top end built tomorrow when I check the squish I think I'll try and do away with the paper gasket 's &
See what the squish is with the copper head gasket & the 3mm ally packer & take it from there .
Ps only gaskit sealant I could get locally was Granville instant gasket will it do , ? or what's the best sealant
To use ?
Thanks once again .

[bazza3004]

Ive built topends in the past with the clear silicon you get from b&q and run them for months without any problems. Theres obviously better sealants available.

[Warkton Tornado No.1]

Post by Vmakgp » Tue Jun 28, 2016 3:31 pm
Cheers 'chaps got the die grinder out today & got stuck in , hopefully get top end built tomorrow when I check the squish I think I'll try and do away with the paper gasket 's &
See what the squish is with the copper head gasket & the 3mm ally packer & take it from there .
Ps only gaskit sealant I could get locally was Granville instant gasket will it do , ? or what's the best sealant
To use ?
Thanks once again .

My advice & experience over 40 or so years is to try & eliminate the head gasket, dependent upon the squish & port timings.

The head to cylinder joint is the area where a gasket is under the most loads as far as heat & pressure compared to the base.

Although I have used silicone sealant for years without issue on the base & the exhaust (with or without a solid copper gasket) I’ve never had a problem with Green Hermetite (other than finding where to buy) with the head/barrel joint, but there are many equivalents.

The only product of that type that I would say to avoid is Blue Hylomar as despite all the claims by the manufacturer, it just seems to roll out of any joint like blue snot.

I hope that helps…

[Vmakgp]

Post by Vmakgp » Tue Jun 28, 2016 3:31 pm
Cheers 'chaps got the die grinder out today & got stuck in , hopefully get top end built tomorrow when I check the squish I think I'll try and do away with the paper gasket 's &
See what the squish is with the copper head gasket & the 3mm ally packer & take it from there .
Ps only gaskit sealant I could get locally was Granville instant gasket will it do , ? or what's the best sealant
To use ?
Thanks once again .

My advice & experience over 40 or so years is to try & eliminate the head gasket, dependent upon the squish & port timings.

The head to cylinder joint is the area where a gasket is under the most loads as far as heat & pressure compared to the base.

Although I have used silicone sealant for years without issue on the base & the exhaust (with or without a solid copper gasket) I’ve never had a problem with Green Hermetite (other than finding where to buy) with the head/barrel joint, but there are many equivalents.

The only product of that type that I would say to avoid is Blue Hylomar as despite all the claims by the manufacturer, it just seems to roll out of any joint like blue snot.

I hope that helps…

Thanks for the advice chaps I built the top end today with alloy packer 2 paper gaskits and .9 copper head gaskit but the squish was only .60 I have another paper gaskit that would get me to the 1.20 squish , but I don't like the idear of three paper & one alloy gaskit down bellow , so I'm thinking of a 3.5 packer & the .9 copper head gaskit ,what's your thoughts ?

[bazza3004]

If the 3.5mm base packer gets the piston were it needs to be the yes go for it.

[Vmakgp]

If the 3.5mm base packer gets the piston were it needs to be the yes go for it.

Cheers bazza

[johnnyXS]

ThreeBond 1211 liquid gasket is the Pros choice ............. or Loctite 515

As WT says avoid Blue Hylomar silicon gasket like the plague. Well known for blocking small oilways and causing engine failure due to oil starvation.

[Vmakgp]

3Bond 1211 liquid gasket or Loctite 515

Cheers fella !

[johnnyXS]

blimey you replied before I'd posted !
The beauty of using ThreeBond (formerly Yamabond) is that it is grey and matches crankcases well

[Vmakgp]

blimey you replied before I'd posted !
The beauty of using ThreeBond (formerly Yamabond) is that it is grey and matches crankcases well

Thanks I will try n get hold of a tube of the three bond though I'm not to fussed about the colour .

[Scooterlam]

Afternoon chaps' I'm looking at matching my small block casing to my GT 186 kit I've marked out on cylinder gaskit face and at the minute the walls are around 7..5 to 8mm I've used the ally packer supplied wich is a decent match to the ports on the GT barrel but I'm reluctant to fully match them as it would take the casings down to 5 mill or just under, so do I not bother at all , or would it be worth maybe taking around 1.5 to 2mm out ? I'm fitting the new GT 60/110 stroke crank and there fore will be using a packer & was worried about taking the width of the gasket face down to much .
Any advise much appreciated .

Has anyone ever quantified the gains of matching case to barrel.
I dont and Im more than happy with the results.

[Vmakgp]

That would be very interesting to now the answer to ' I fitted the top end on today with a 3.5 packer ,& head gaskit ,squish was 1.25 , and porting times matched those supplied by gran turismo found the Tdc and marked mag housing for timing Mark , just waiting for BGM clutch to arrive then onto fitting the Casa tronic ignition new sprocket n chain then hopefully get the engine dropped in and onto wiring

[Eden]

Afternoon chaps' I'm looking at matching my small block casing to my GT 186 kit I've marked out on cylinder gaskit face and at the minute the walls are around 7..5 to 8mm I've used the ally packer supplied wich is a decent match to the ports on the GT barrel but I'm reluctant to fully match them as it would take the casings down to 5 mill or just under, so do I not bother at all , or would it be worth maybe taking around 1.5 to 2mm out ? I'm fitting the new GT 60/110 stroke crank and there fore will be using a packer & was worried about taking the width of the gasket face down to much .
Any advise much appreciated .

Has anyone ever quantified the gains of matching case to barrel.
I dont and Im more than happy with the results.

yes and if you did you would be even happier than you currently are

[Adam_Winstone]

I match all of my barrels to my casings, however, I never take out more than I need to for a better match/flow. Decades ago I started to open transfers out too far, matching the casing feeds to them, then finding (having never suffered base gasket failures previously) that I ran into repeat failures of base gaskets blowing. This then meant that I had to change over to no gasket + sealant, which returned me to reliable running, however, it meant that paper base gaskets were no longer an option for lifting the barrel to get squish/port position where I wanted it.

Based on the above, combined with performance gains being negligible, I've stuck with not going too thin at the transfer edge and just getting the flow right, which means that paper base gaskets remain viable and performance is good.

Unfortunately, I now have a couple of casings with 3mm edges that can no longer be used with paper gaskets as they do blow

Adam

[johnnyXS]

pity somebody hasn't some pictures to post as this is a very interesting and topical subject . I believe and hope that Scootering will be covering this in future editions.

I can see the benefit of matching the transfer ports of the casing to the 186 engine but not if it leaves insufficient mating surface on the crankcase for reliable sealing.

Why do the 186 engine castings have such over-sized transfer ports when its surely known that the small block crankcase doesn't match and would require so much material ground away to achieve a match ?

It might be interesting to build up the transfer ports on a 186 so that less material needs grinding out of the crankcase to achieve a match and best flow characteristics. Then do a comparison to see how much HP is actually lost through the slight decrease in transfer port size.

The reason that I ask this is because it seems to me that we are all just assuming that these 186 cylinders have been produced to correct tolerances and with adequate quality control . I would question that they have .......if it is necessary in every instance to grind out your stock small block casing to match the transfer ports to such an extent that there is less than adequate material left on the casing face to be able to form an adequate seal.

Too often these days manufacturers cast parts for years without any quality control checks and small errors become larger over time .

To take a case in point ...have a look at the the 20 + 'damaged' Sil crankcases and cylinders currently for sale on the Scooter Restoration site . Most if not all of the faults are due to inaccurate machining and inadequate quality control and those are just the tip of the iceburg.

With most of our parts currently being manufactured in India, I don't believe we should take anything for granted. I for one would question that the GT186 cylinders are being manufactured to the correct specification and tolerances if it is necessary to remove so much material from the stock crankcase that it is then not possible to achieve a satisfactory and reliable compression seal